<a href="http://www.sina.com.cn" onClick="return click_handler()">
  Click this "javascript:void(0)" link.
</a>
<p>
<img src="dog.jpg" onDblClick="this.src='dog1.jpg'">
<script>
  function click_handler()
  {
    alert("You Click")
    return false 
  }
</script>
